synthesis and characterization of interpenetrating polymer

Journal of Saudi Chemical Society (2013) xxx, xxx–xxx

King Saud University

Journal of Saudi Chemical Society

www.ksu.edu.sawww.sciencedirect.com

ORIGINAL ARTICLE

Synthesis and characterization of interpenetrating

polymer networks from transesterified castor oil

based polyurethane and polystyrene

Vivek J. Dave, Hasmukh S. Patel *

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India

Received 25 April 2013; accepted 28 August 2013

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KEYWORDS

Interpenetrating network;

Polystyrene;

Polyurethanes

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Abstract A series of two component interpenetrating polymer networks (IPN) of modified castor

oil based polyurethane (PU) and polystyrene (PS) were prepared by the sequential method. Castor

oil was modified by triethanolamine by means of transesterification and designated as transesterified

castor oil (TCO). The polyurethane network was prepared from transesterified castor oil (TCO)

with the isophoronediisocyanates (IPDI) by using dibutyltindilaurate (DBTDL) as catalyst. Simul-

taneously styrene was added with benzoyl peroxide (BPO) as initiator and N,N0-Dimehtylaniline as

coinitiator. Diallylphthalate was added as a crosslinking agent to form IPN and finally cast into

films. To cast the film, the mixture (IPN) was poured in the glass cavity with pourable viscosity free

from air bubbles. A series of two component interpenetrating polymer networks were prepared by

varying % weight ratio of both polyurethane and polystyrene. These films were characterized by

FT-IR, dynamic mechanical analysis (DMA), thermogravimetry analysis (TGA), morphology

was measured by scanning electron microscopy (SEM). FT-IR have given the conformation of

IPN formation. DMA results have shown much increase in the value of tand and a decrease in

the value of Tg by increasing the anount of Styrene.ª 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Interpenetrating polymer networks (IPN) can be elaborated asspecial class of the polymers in which there is a combination of

692 226856x220.

om (H.S. Patel).

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V.J., Patel, H.S. Synthesis and charstyrene. Journal of Saudi Chemica

two polymers in which one is synthesized or polymerized in the

presence of other (Chen et al., 2011; Ajithkumar et al., 2000).IPN is a different way to combine two different polymers otherthan physical blends and copolymerization. For the synthesisof any IPN it should have three conditions (i) the two polymers

are synthesized and/or crosslinked in the presence of the other,(ii) the two polymers have similar kinetics, and (iii) the twopolymers are not dramatically phase separated (Jimenez

et al., 2009).There is no involvement of covalent bonds be-tween two polymers; hence monomer A reacts only withmonomer A, while on the other hand monomer B reacts only

with monomer B. The resulting material does not get dissolved

ing Saud University.

acterization of interpenetrating polymer networks from transesterifiedl Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.08.001

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http://dx.doi.org/10.1016/j.jscs.2013.08.001


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2 V.J. Dave, H.S. Patel

in the solvents but it gets swelled (da Cunha et al., 2004). IPNsoffer the possibility of combining in a network form whichotherwise are non-compatible polymers with opposite proper-

ties (Pissis et al., 2002). IPN formulation is a useful method todevelop a product with excellent physico-mechanical proper-ties than the normal polyblends. IPN is also known as the

polymer alloys and it is one of the fastest growing areas of re-search in the field of polymer blends since last two decades.

IPN can be made in many different ways. It can be defined as

sequential and simultaneous IPN depending on how the poly-merization has been carried out. Another kind of IPN is the la-tex IPN when IPN is in the form of latex; hence it also called asinterpenetrating elastomeric networks (IEN) (Jaisankar et al.,

2013). When filmmade with a network of one polymer predom-inantly on one surface and a network of another polymer on theother surface there is a gradient inside the film which is called

gradient IPN. While among the combination of two polymersof IPN, when one is crosslinked and the another is linear orbranched it is known as semi- IPN (Athawale et al., 2003).

The application of green resources in the field of polymers isthe centre of attraction for many researchers; because they pos-sess potential for substitution of petrochemical derivatives.

Most of the attention has been focused on the research anddevelopment of newer materials from renewable materials(Lan et al., 2012). Among all vegetable oils, one of the most nat-urally and abundantly occurring oils is castor oil. Castor oil

based polyols are nowadays becoming an important raw mate-rial for the polyurethane since it is environmentally friendly andcost competitive (Mutlu and Meier, 2010). In recent time IPNs

synthesized from castor oil have been paid good attention in theindustrial applications (Begum and Siddaramaiah, 2004). Cas-tor oil is easily available as a dominating product from the cas-

tor seeds. Castor oil is the only naturally occurring polyol thatpossesses hydroxyl groups. Castor oil based polyurethane is awidely useful material as it possesses good flexibility and elas-

ticity because of the presence of a long fatty acid chain andleads itself as a thermosetting type material due to its trifunc-tional nature (Zhang and Zhou, 1999; Gao and Zhang, 2001;Valero et al., 2009). There are so many literatures on modified

Scheme 1 Modification of castor oil with

Please cite this article in press as: Dave, V.J., Patel, H.S. Synthesis and chacastor oil based polyurethane and polystyrene. Journal of Saudi Chemica

castor oil polyurethane, but IPNs of modified castor oil poly-urethane have not been paid much attention (Kumar et al.,1987; Patel and Suthar, 1989; Pandit et al., 1994; Bai et al.,

1997; Siddaramaiah and Mallu, 1998; Siddaramaiah and Mal-lu, 1999). Only a few instances have shown the use of transeste-rified castor oil by glycerol and pentaerythritol for the synthesis

of IPNs (Sanmathi et al., 2004; Valero et al., 2009, 2010). Thereis no report found regarding transesterification of castor oilwith triethanolamine for IPN synthesis. So it was thought to

study IPNs from triethanolamine based transesterified castoroil polyurethane. The aim of our present work is to study ther-mal, damping and morphological properties of IPN films. Thusthe present work comprises the transesterification of castor oil

by triethanolamine followed by polyurethane formation andfinally IPN synthesis by adding styrene monomer.

2. Experimental

2.1. General

Castor oil was purchased from local market and found to con-tain hydroxyl value 163, corresponding to 2.7 hydroxyl groups

per mole of castor oil according to the literature method (Erenet al., 2006). Isophoronediisocyanate (IPDI) was purchasedfrom Aldrich. Triethanolamine was purchased from SDFCL

and was used without further purification. Dibutyltindilaurate(DBTDL) was purchased from HIMEDIA. Benzoyl peroxide(BPO) was obtained from SDFCL. Styrene was obtained from

Samir Tech. Chem. Ltd. and was used by removing inhibitorsin it. Diallyl phthalate was obtained from Sigma Aldrich.

2.2. Transesterification of castor oil

Transesterification was performed in a 500 ml three neckedflask and equipped with mechanical stirrer, thermometer pock-et, and water condenser. One mole of triethanolamine was

mixed with 1.0 mol of castor oil. Then 0.2% lead oxide(PbO) in relation to the total mass of the reactants was added

triethanolamine by transesterification.

racterization of interpenetrating polymer networks from transesterifiedl Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.08.001


Scheme 2 Synthetic route of PU network from transesterified

castor oil (TCO).

Synthesis and characterization of interpenetrating polymer networks from transesterified castor oil 3

as the catalyst. The reaction was performed at 150 �C for 2 h.The transesterification was verified by thin layer chromatogra-

phy using a 1:1 solvent mixture (diethylether:cyclohexane).The obtained modified castor oil was named as TCO and thesynthetic route is shown in Scheme 1. The change in viscositywas measured at the end of the reaction by Brookfield viscom-

eter (See supplementary data).

Figure 1 FT-IR spectrum

Please cite this article in press as: Dave, V.J., Patel, H.S. Synthesis and charcastor oil based polyurethane and polystyrene. Journal of Saudi Chemica

2.3. Synthesis of simultaneous interpenetrating polymernetworks

A calculated amount of isophoronediisocyanate (IPDI) wastaken in a three necked flask which was equipped with

mechanical stirrer and water condenser and a correspondingamount of triethanolamine modified castor oil (TCO) wasadded gradually in the presence of dibutyl tindilaurate(DBTDL) as catalyst. The reaction was performed at 45 �C–50 �C for 2 h. The reaction was monitored at regular timeinterval by measuring the % NCO value (See Supplementarydata). During the preparation of polyurethane network, sty-

rene was added along with the initiator benzoyl peroxide(BPO), coinitiator N,N0-Dimethylaniline and diallyl phthalate(cross linking agent) to form IPN in the form of casted films.

As the reaction mixture (IPN) became pourable viscous liquid,it was poured into the glass cavity without remaining air bub-ble and rest of the reaction was allowed to proceed at room

temperature. It was kept at room temperature for 24 h for cur-ing. Then yellow tough films were observed. A series of IPNsof different compositions were obtained by varying the weightof polyurethane and styrene monomer following the same pro-

cedure. The finished films were cut in desired shapes for furtherstudy and characterization. The synthetic route of PU networkis shown in the reaction in Scheme 2 and synthetic route of

IPN from PU network with PS is shown in Scheme 3.

2.4. Characterization of IPN films

2.4.1. FT-IR studies

The FTIR spectra of TCOPU/PS IPN were obtained by usingPerkin Elmer spectrometer. The samples were ground with

KBr and were used in the form of pellet.

2.4.2. Dynamic mechanical analysis

The dynamic mechanical analysis (DMA) was carried out onDMA 242 C analyser with auto tension mode over a tempera-ture range of 25 �C–200 �C at a heating rate of 10 �C/min at

of TCOPU/PS IPN.



Scheme 3 Synthetic route of IPN from

Table 1 DMA data of TCOPU/PS IPNs with different component ratios at 1 Hz frequency.

No % Weight components Temp. range (C�) tand tand (max) Tg in (�C)

% TCOPU % PS

IPN-1a 90 10 59.7–153.5 0.553 103.8

IPN-1b 80 20 53.1–153.5 0.616 100.5

IPN-1c 70 30 56.4–156.2 0.701 96.3

IPN-1d 60 40 50.6–142.6 0.710 95.2

IPN-1e 50 50 42.8–163.3 0.812 94.2

IPN-1f 40 60 55.4–156.3 0.819 93.4

IPN-1g 30 70 51.3–165.7 0.835 92.1

IPN-1h 20 80 58.9–167.8 0.853 88.9

IPN-1i 10 90 60.8–168.1 0.856 88.4

Figure 2 DMA curve of TCOPU/PS IPNs with component ratio

from 90:10 to 10:90.



1 Hz frequency. The samples were cut in a rectangular bar(5 mm · 1 mm · 5 mm).

2.4.3. Thermogravimetric analysis

For thermogravimetric analysis (TGA), the decompositionprofile of the IPN films was thermogravimetrically analysedwith a Universal V2.6D TA Instrument. Film samples ranging

from 4 to 6 mg were placed in a platinum sample pan andheated from 30 �C to 600 �C under an N2 atmosphere at aheating rate of 10 �C/min, and the weight loss was recorded

as a function of temperature.

2.4.4. SEM analysis

Scanning electron microscopy (SEM) was performed for sam-

ple microstructural analysis on an electron microscope JoelJSM-6380 LV model. The voltage acceleration was of 15 Kw.

PU network (TCOPU) with styrene.



Figure 3 TGA thermograms for (A) IPN 1a (B) IPN 1e (C) IPN 1i (D) Pure PS.

Table 2 Data obtained for TGA thermograms of various

samples.

IPN system Temperature 20% Temperature 50% Temperature 80%

Loss/�C Loss/�C Loss/�C

IPN 1a 290 370 400

IPN 1e 270 310 390

IPN 1i 260 290 375

Pure PS 235 260 320


3. Results and discussion

The obtained modified castor oil is the mixture of mono-, di-

glycerols and was used for the PU preparation for the IPNwithout further purification. An important characteristic havefound from the modification is the hydroxyl value of this mod-

ified castor oil increases from 163 mg KOH/gm to 321 mgKOH/gm.

3.1. Structural analysis of IPN

Fig. 1 has displayed theFTIR spectrumofTCOPU/PS IPN.Thecharacteristic pick at 1700–1721 cm�1 indicates the presence for>C‚O (Carbonyl) in urethane linkage. N–H stretching

vibrations of the urethane linkage give the broad band around3341–3343 cm�1. Weak bands around 1018–1023 cm�1 revealthe presence of the aromatic ring of polystyrene. The absence

of the peak around 2260 cm�1 shows that each –NCO groupshave reacted with –OH group of polyol and converted intourethane linkage. The spectrum displays the sharp peak around

2915–2928 cm�1 that attributes to the presence of the methylenegroup in polystyrene. The peak around 1233–1263 cm�1 may beattributed to –CH2 of aliphatic chain of polyurethane.

3.2. Dynamic mechanical analysis

Table 1 and Fig. 2 show the data of TCOPU/PS IPNs differentcomponents at 1 Hz and DMA curve. We have tried to find

out the various mechanical damping properties of IPNs bytaking different % weight ratio of both polymers used in theIPN preparation. Dynamic mechanical analysis or dynamic

mechanical thermal analysis (DMTA) is a useful method forthe determination of elastic and loss modulus of polymers asa function of temperature, frequency or time, or both. The dy-

namic mechanical analysis was characterized by storage mod-ulus (E0), loss modulus (E00) and loss factor (tand), which can


be elaborated by the ratio of loss modulus to storage modulus.All the shown three parameters are the function of tempera-

ture and frequencies. Normally magnitude of tand can be usedto predict the damping behaviour of the polymeric material(Ping and Wang, 2010). This property can be the essential

property for the material selection, as an example we can con-sider shock absorber property, higher values of damping leadto the higher energy absorption. Generally materials which

are having a high and wide loss factor peak can be used asgood damping materials.

It can be seen from Fig. 2 that there is much influence of the

value of tand as the % weight ratio of polystyrene increaseswhile Tg gets decreased as increasing the % weight ratio ofpolystyrene. It can also be seen from Fig. 2 that temperaturefor peak of the tand becomes much lower as the PS content in-

creases. It can also be observed from the figure that all thecompositions are showing the single value of tand. This isattributed to the homogeneous composition (Chen et al.,

2010).

3.3. Thermogravimetric analysis

Thermal degradation properties of IPN 1a, IPN 1e, and IPN 1iare assessed by TGA. Fig. 3 and Table 2 describe the thermaldegradation of IPNs at various temperatures. All the IPNs



Figure 4 SEM micrographs of IPN 1a, IPN 1e and IPN 1i.


were found almost thermally stable up to 200 �C. For IPN 1a,IPN 1e and IPN 1i 20% weight loss occurs at 290 �C, 270 �Cand 260 �C. This mass loss is due to evaporation of solventmolecules, elimination of smaller groups and volatile matters.For IPN 1a, IPN 1e and IPN 1i 50% mass loss occurs at

370 �C, 310 �C and 290 �C. At this temperature range IPN1a seems relatively more stable, while 80% weight loss for allthe three IPNs occurs at 400 �C, 390 �C and 375 �C. This

may be attributed to the decomposition of the main functionalgroups such as >NH and >C‚O of polyurethane anddecrosslinking of polystyrene. However, there is not muchchange in thermal stability of all IPNs with an increase in

the content of polystyrene. Thermal properties of all the IPNsare found to be much better than that of the homopolymerpolystyrene.

3.4. Phase morphology

The morphology of the IPNs was studied from their SEM

micrographs, which are shown in Fig. 4. For the same purposewe have chosen in the random manner, IPN 1a, IPN 1e andIPN 1i. We observed the homogeneity in each specimen, which

indicates the interpenetration of the phase domains of TCOPUand PS.

4. Conclusion

Castor oil is a good renewable resource and it has been utilizedfor so many applications like lubricants, paints, coating etc.IPNs from castor oil have been developed for the diverse appli-

cations. IPNs prepared form transesterified castor oil showedimproved properties due to more crosslinking density due toan increase in hydroxyl content. The FT-IR spectrum of

TCOPU/PS IPNs gives the conformation of the formation ofIPN. The storage modulus and tand of each TCOPU/PSIPN films were determined as a function of temperature. The

TgS of the films decreased with the increase in the amount ofpolystyrene used in the synthesis. It was also shown that thereis an increase in the tand peak by increasing the amount of

polystyrene used. The single values of Tg attributes to the factthat no phase separation occurred in the synthesized films. Allthe IPNs show the better thermal stability than that of purepolystyrene. Homogeneity in each species from SEM analysis

indicates the interpenetration of both networks. It can be con-cluded that it is possible to obtain transesterified castor oilbased IPNs with good thermal properties.


Acknowledgement

Authors are grateful to Department of Chemistry, Sardar Pa-tel University, Vallabh Vidyanagar for providing researchfacilities. One of our authors is thankful to University GrantCommission (UGC), New Delhi to provide meritorious re-

search fellowship.

Appendix A. Supplementary data

Supplementary data associated with this article can be found,in the online version, at http://dx.doi.org/10.1016/j.jscs.2013.08.001.

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